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<head><meta charset="utf-8"><title>What is the fuzzy category used for? · t-compiler/help · Zulip Chat Archive</title></head>
<h2>Stream: <a href="https://rust-lang.github.io/zulip_archive/stream/182449-t-compiler/help/index.html">t-compiler/help</a></h2>
<h3>Topic: <a href="https://rust-lang.github.io/zulip_archive/stream/182449-t-compiler/help/topic/What.20is.20the.20fuzzy.20category.20used.20for.3F.html">What is the fuzzy category used for?</a></h3>

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<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/182449-t-compiler/help/topic/What%20is%20the%20fuzzy%20category%20used%20for%3F/near/245558408" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Kjetil Kjeka <a href="https://rust-lang.github.io/zulip_archive/stream/182449-t-compiler/help/topic/What.20is.20the.20fuzzy.20category.20used.20for.3F.html#245558408">(Jul 10 2021 at 16:01)</a>:</h4>
<p>Would anyone mind give me a quick explanation of what the "fuzzy category" in <code>rustc_trait_selection::traits::error_reporting::fuzzy_match_tys</code> is used for?</p>
<p><a href="/user_uploads/4715/IclCbgxWABzOt7dEPxj3aumU/image.png">image.png</a></p>
<div class="message_inline_image"><a href="/user_uploads/4715/IclCbgxWABzOt7dEPxj3aumU/image.png" title="image.png"><img src="/user_uploads/4715/IclCbgxWABzOt7dEPxj3aumU/image.png"></a></div><p>I'm completely new to rustc and trying to investigate how hard it would be to implement a new custom DST (<a href="https://internals.rust-lang.org/t/should-array-view-be-an-internal-type/14983/10">https://internals.rust-lang.org/t/should-array-view-be-an-internal-type/14983/10</a>)</p>
<p>The type (an array view) is basically a DST that owns structured but non-contiguous  memory, and I'm wondering if it needs to be Some(6) together with slice and array or if due to being non-contiguous needs a seperate "fuzzy category"?</p>



<a name="245560860"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/182449-t-compiler/help/topic/What%20is%20the%20fuzzy%20category%20used%20for%3F/near/245560860" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Hill <a href="https://rust-lang.github.io/zulip_archive/stream/182449-t-compiler/help/topic/What.20is.20the.20fuzzy.20category.20used.20for.3F.html#245560860">(Jul 10 2021 at 16:57)</a>:</h4>
<p>It looks like that method is used only for diagnostics</p>



<a name="245560875"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/182449-t-compiler/help/topic/What%20is%20the%20fuzzy%20category%20used%20for%3F/near/245560875" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Hill <a href="https://rust-lang.github.io/zulip_archive/stream/182449-t-compiler/help/topic/What.20is.20the.20fuzzy.20category.20used.20for.3F.html#245560875">(Jul 10 2021 at 16:57)</a>:</h4>
<p>You should just be able to return <code>None</code> if you're adding a new type</p>



<hr><p>Last updated: Aug 07 2021 at 22:04 UTC</p>
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